1. Field of the Invention
The present invention relates to a method and an apparatus for flatly polishing a plated film and an insulating film formed on a surface of a wafer, for example.
2. Description of the Related Art
Along with higher integration and further down-sizing of semiconductor devices, contraction of wire diameter and wiring pitch as well as multiplication of wiring layer have been promoted to intensify importance of multiple-layer wiring technology in the semiconductor manufacturing process.
Conventionally, aluminum has mainly been used for composing multiple-layer wiring of semiconductor devices. On the other hand, in order to suppress delayed transmission of signal, in the modern design rule dealing with a maximum of 0.18 xcexcm rule, such a wiring process by way of replacing aluminum with copper has been developed in recent years. Utilization of copper for wiring provides bilateral advantage in terms of low electric resistance and high resistance against electromigration.
In such a process for applying copper to the wiring for example, initially, metal is embedded in slit-form wiring pattern formed in an inter-layer insulating film, and then wiring is formed by removing excessive metal film via a chemical mechanical polishing (CMP) method. Recently, such a wiring process called xe2x80x9cdamascenexe2x80x9d process has become influential. According to the xe2x80x9cdamascenexe2x80x9d process, an etching process of wiring is not required. And yet, since the upper inter-layer insulating film is leveled off naturally, the xe2x80x9cdamascenexe2x80x9d process advantageously simplifies processing steps.
Further, when introducing xe2x80x9cdual damascenexe2x80x9d process which initially forms wiring slit and contact holes through the inter-layer insulating film at the same time and then embeds both of them with metal, it is possible to drastically save the steps of the wiring processes.
Referring now to the accompanying drawings, a process for forming wiring by applying the above xe2x80x9cdual damascenexe2x80x9d process is exemplified below. Note that the wiring is formed with copper in this example.
Initially, as shown in FIG. 39A, an inter-layer insulating film 2 made of silicon oxide is formed on a silicon semiconductor substrate 1 having properly formed impurities-diffused domain (not shown) therein via a low-pressure chemical vapor deposition (CVD) process, for example.
Next, as shown in FIG. 39B, by applying the known photolithographic technique and etching process, a contact hole CH linked with the impurities-diffused region of the semiconductor substrate 1 and slit M for accommodating wiring of a predetermined pattern electrically linked with the impurities-diffused region of the same semiconductor substrate 1 are respectively formed.
Next, as shown in FIG. 39C, a barrier film 4 formed on the surface of the inter-layer insulating film 2, and yet, the same barrier film 4 is also formed through the contact hole CH and inside of the slit M. The barrier film 4 is formed with tantalum Ta, Titanium Ti, TaN, and TiN by applying a known sputtering process. When copper is used for composing wiring and silicon oxide for composing an inter-layer insulating film 2, since copper significantly diffuses into silicon with a substantial diffusion coefficient, copper is easily oxidized. To prevent copper from being oxidized, the barrier film 4 is necessarily formed.
Next, as shown in FIG. 39D, a seed film 5 is formed on the barrier film 4 by way of depositing copper on the barrier film 4 by applying a known sputtering process.
Next, as shown in FIG. 39E, in order to fully embed the contact hole CH and the slit M with copper, a copper film 6 is formed by applying a plating process, or a chemical vapor deposition (CVD) process, or a sputtering process, for example.
Next, as shown in FIG. 39F, excessive portion of the copper film 6 and the barrier film 4 is removed via a chemical mechanical polishing (CMP) process to level off the copper film 6.
By implementing the above serial processes, a copper wiring 7 and a contact 8 are eventually formed. By way of repeatedly implementing the above serial processes on the copper wiring 7, multiple-layer wiring is formed.
When implementing the above-described polishing process, a surface-leveling polishing apparatus is utilized.
FIG. 40 presents a schematic perspective view of a conventional surface-leveling polishing apparatus. The conventional surface-leveling polishing apparatus 20 comprises the following: a rotatable disc-form stationary base 22 adhered with a polishing cloth 21 on the upper surface; a rotatable and vertically movable (in the Z direction) disc-form mounting plate 23 for holding a wafer 10 at the bottom surface; and a nozzle 24 for feeding polishing solution P onto the polishing cloth 21.
When operating the above-referred conventional surface-leveling polishing apparatus shown in FIG. 40, initially, a front surface of the wafer 10 provided with the copper film 6 requiring formation of multi-layer wiring pattern is set prone, and then, the back surface of the wafer 10 is adhered to the bottom surface of the mounting plate 23 or absorbed onto the bottom surface via vacuum pressure.
Next, while jointly rotating the stationary base 22 and the mounting plate 23, polishing solution P is poured onto the polishing cloth 21 via the nozzle 24.
Next, by lowering the mounting plate 23, the front surface of the wafer 10 is pressed against the polishing cloth 21 to polish the copper film 6 requiring formation of the multiple-layer wiring pattern thereon.
Nevertheless, the above conventional surface-leveling polishing apparatus 20 still has a technical problem to solve because polishing amount of the copper film 6 requiring formation of multi-layer wiring pattern thereon still remains unstable inasmuch as the polishing operation is subject to time-control whereby failing to correctly determine actually polished amount until terminating the polishing operation.
Further, polishing precision is variable by actual condition of the polishing cloth 21 whereby unstableness constantly remains in the polishing operation. To secure polishing precision, in many cases, polishing precision is dependent on skill and perception of well-experienced operators.
In addition, because of difference in the removal effect between the inter-layer insulating film 2, the copper film 6, and the barrier film 4, various technical problems such as dishing, erosion (thinning), or recess are apt to be generated.
As shown in FIG. 41A, the above-referred dishing designates such a phenomenon in which, if such a wiring 7 having about 100 xcexcm of width is present in the design rule for ruling a maximum of 0.18 xcexcm of width, for example, a center portion of the wiring 7 is excessively removed to generate a recessed portion therein. Once the dishing phenomenon is ever generated, because of shortage of sectional area of the wiring 7, it will cause the wiring 7 to generate an improper electrical resistance value. The dishing phenomenon is apt to be generated when relatively soft copper or aluminum is used for composing the wiring.
On the other hand, as shown in FIG. 41B, the above-referred erosion designates such a phenomenon in which a specific portion provided with a very high pattern density containing wiring having 1.0 xcexcm of width at 50% density within 3000 xcexcm of range is excessively removed. Once erosion ever takes place, because of short sectional area of the wiring, it will also cause the wiring to generate an improper electrical resistance value.
Further, as shown in FIG. 41C, the above-referred recess designates such a phenomenon in which stepwise difference is generated as a result of the lowered wiring 7 at the interface between the inter-layer insulating film 2 and the wiring 7. Like the above cases, because of short sectional area of the wiring 7, the wiring 7 will generate an improper electrical resistance value.
On the other hand, when applying the above-referred xe2x80x9cdamascenexe2x80x9d method or xe2x80x9cdual damascenexe2x80x9d method in particular, inasmuch as the slit for wiring or the wiring slit and the contact hole are simultaneously embedded with copper, excessive copper film 6 generates a substantial film thickness, and yet, inasmuch as projections and recessed portions are generated on the surface of the copper film 6, it is necessary to relax the initial stepwise difference by efficiently removing the excessive copper film 6 via the chemical mechanical polishing (CMP) method.
Accordingly, it is so required that the polishing rate representing a removable amount per unit time should be a minimum of 500 nm/minute, for example. In order to secure the required polishing rate, such a method by way of raising processing pressure against each wafer, utilization of such a chemical solution with stronger etching effect, or such a method by way of raising the number of the rotation of polishing tools, are conceived. However, even when applying any of these methods for improving polishing rate, in terms of precision, it is known that capability for relaxing stepwise difference, in other words, leveling capability, is lowered.
Further, as shown in FIG. 42, scratch (SC) and/or chemical damage (CD) are easily generated on the surface of wiring. In particular, soft copper material easily incurs such damage. Because of this, faulty phenomena such as opened wiring, short-circuited wiring, improper electrical resistance value of the wiring, are apt to be generated. Further, when applying any of the above-cited processing methods to improve the polishing rate, there is such a disadvantage in which crack, stripping of inter-layer insulating film, dishing, erosion, and recessed portions, are increasingly generated.
On the other hand, in order to eliminate unstableness caused by variable condition of the polishing cloth 21 and minimize the dependence on experienced skill and perception of experienced operators as much as possible, such a polishing apparatus capable of securing satisfactory leveling effect in the chemical mechanical polishing process by means of a rigid-type polishing wheel has been realized so that uniform effect of correction via software controlling method by way of dispensing with experienced human skill can be materialized.
Nevertheless, actually, the above-cited uniform effect of correction via utilization of the above polishing apparatus is still dependent on experienced skill and perception of experienced operators to a large extent, and thus, substantial skill is still required for preparation of so-called recipe.
When operating the above polishing apparatus to execute such a process to remove excessive copper film by causing an annular-shaped wheel to be abutted with a circular-form wafer partially, since the annular-shaped wheel not only strictly executes partial processing of the circular wafer, but it also processes a certain area of the wafer, it makes it difficult to properly adjust recipe for partially correcting removable amount of excessive copper film.
In addition, when varying tilt angle of the main shaft, even such a well-experienced operator often finds unexpected result from the correction process, and thus, in terms of the uniform effect of correction, actually, variation of the removable amount of copper film against a variety of input parameters is not yet determined quantitatively.
Concretely, when operating such a conventional polishing apparatus, in order to improve and maintain uniform effect of correction on the way of continuously processing a wafer, it is imperative that change and correction be executed against a variety of processing parameters repeatedly in accordance with forecast based on experiences of operators. Accordingly, process margin in the production of semiconductor devices is not determined by the applied device system, but it still largely hinges on expertise of operators.
The present invention has been achieved in consideration of the above circumstances. The object of the present invention is to provide such a method and an apparatus for polishing a plated film and an insulating film formed on a wafer surface, which are capable of stably improving polishing rate and securing high processing precision while maintaining capability to relax initial stepwise difference, i.e., projections and recessed portions, in the course of leveling off metallic film such as copper wiring while steadily preventing faulty phenomenon such as dishing and erosion from occurrence without being swayed by skilled expertise of operators.
In order to achieve the above object, the present invention provides a method for flatly polishing surface of a polishing object by shifting surfaces of a polishing means and a polishing object relative to each other in a predetermined direction based on a polishing condition prescribed by processing pressure P, relative velocity xe2x80x9cvxe2x80x9d between the polishing means and the polishing object, and polishing time xe2x80x9ctxe2x80x9d. Initially, this method computes distribution of the removable amount of copper material on the surface of the polishing object generated by influence of a variety of processing parameters based on a proportional constant xe2x80x9ckxe2x80x9d determined by the polishing status and also based on the Preston""s equation prescribed by the polishing condition. Next, the method computes a proportional constant xe2x80x9ckxe2x80x9d capable of generating uniformly flat distribution of the removable amount computed by Preston""s equation. Next, the method computes distribution of the removable amount based on a proportional constant xe2x80x9ckxe2x80x9d as a fixed value. Finally, the method sets a polishing condition that enables distribution of the removable amount to secure uniform levelness when the above-referred proportional constant xe2x80x9ckxe2x80x9d functions as a fixed value.
Further, when implementing the present invention, the above-referred polishing condition based on the Preston""s equation is set by prescribing the polishing time xe2x80x9ctxe2x80x9d when the above-referred processing pressure P and the relative velocity xe2x80x9cvxe2x80x9d are respectively utilized as a fixed value.
Further, when implementing the present invention, the above-referred polishing condition based on the Preston""s equation is set by prescribing the above-referred relative velocity xe2x80x9cvxe2x80x9d when the above-referred processing pressure P and the polishing time xe2x80x9ctxe2x80x9d are respectively utilized as a fixed value.
Further, in the present invention, the above-referred polishing object is substantially a semiconductor wafer itself, wherein polishing of the wafer is executed in the direction of relaxing peak of polishing directivity prescribed at the time of polishing by the polishing means or in the direction of averaging polishing direction in the center portion of the wafer.
Further, in the present invention, initially, variation of superficial reflectivity of the above-referred polishing object is detected, and then, based on the detected value, remaining unscraped portion of the polishing object is identified. Finally, practicable polishing condition against the remaining unscraped portion and such portions other than the remaining unscraped portion are automatically generated.
Further, in the present invention, by way of measuring film thickness of the polishing object, such a portion requiring removal of excessive copper material is detected, and then, based on the detected value, practical condition for processing the detected portion is automatically generated.
Further, in the present invention, the above-referred polishing object comprises copper wiring. By way of measuring variation of sheet resistivity during off-line period, parameter necessary for correcting the removable amount is calculated, and then, by way of automatically correcting the removing condition, a proper condition for securing uniformity of the removable amount is prepared.
Further, the present invention provides such a polishing apparatus which initially shifts surfaces of a polishing means and a polishing object in a predetermined direction relative to each other, and then flatly polishes surface of the polishing object by applying a polishing condition prescribed by the preset processing pressure P, relative velocity xe2x80x9cvxe2x80x9d between the polishing means and the polishing object, and polishing time xe2x80x9ctxe2x80x9d. The polishing condition is set at a specific value enabling distribution of a second removable amount to secure uniform levelness when distribution of a first removable amount on the surface of the polishing object applies proportional constant xe2x80x9ckxe2x80x9d for securing uniform levelness as a fixed value, where the distribution of the first removable amount on the surface of the polishing object is generated by influence of a variety of processing parameters computed by the proportional constant xe2x80x9ckxe2x80x9d determined by the polishing condition and in accordance with Preston""s equation prescribed by the polishing condition.
Further, the polishing apparatus provided by the present invention comprises detecting means for detecting variation of superficial reflectivity of the above-referred polishing object and controlling means which, based on the detected value, identifies remaining unscraped portion of the polishing object and then automatically generates a proper polishing condition against the remaining unscraped portion and such portions other than the remaining unscraped portion.
According to the present invention, distribution of the removable amount of excessive copper film on the surface of a polishing object generated by influence of a variety of processing parameters is computed based on a proportional constant xe2x80x9ckxe2x80x9d determined by the polishing status and in accordance with Preston""s equation prescribed by processing pressure P, relative velocity xe2x80x9cvxe2x80x9d between the polishing means and the polishing object, and the polishing time xe2x80x9ctxe2x80x9d.
Next, such a proportional constant xe2x80x9ckxe2x80x9d enabling distribution of the removable amount to secure uniform levelness is computed.
Next, such a distribution of the removable amount by applying the proportional constant xe2x80x9ckxe2x80x9d as a fixed value is computed to enable establishment of such a specific polishing condition for enabling the distribution of the removable amount to secure uniform levelness.
Finally, by applying the polishing condition set by the polishing means, surface of the polishing object is properly scraped off.
As is apparent from the above description, according to the present invention, the inventive polishing method and apparatus provide such a useful advantage by way of assuredly preventing dishing and erosion from occurrence without being swayed by skill and perception of experienced operators, and yet, in the course of leveling off copper film or the like via a polishing process, it is possible to improve the polishing rate while preserving initial capability to relax stepwise difference caused by projections and recesses, whereby making it possible to constantly achieve very high processing precision.